JP7322130B2 - image forming device - Google Patents

Description

The present invention improves the glossiness of a toner image by reheating a fixed toner image on a recording material or a fixing device installed in an image forming apparatus such as a copier or printer using an electrophotographic method or an electrostatic recording method. It relates to an image heating device such as a glossing device that improves the The present invention also relates to an image forming apparatus including this image heating device.

As means for protecting an image heating apparatus having a heating element, there is a method using a temperature detecting element. When the temperature based on the temperature information of the temperature detection element is abnormal, the abnormal temperature detection means outputs an electrical signal. In response to this output signal, the cutoff means cuts off the power supply to the heating element to prevent damage to the device. Japanese Patent Application Laid-Open No. 2002-200001 proposes a method of eliminating the need to secure a distance between the heat generating element on the primary side and the temperature detecting element, thereby realizing both a reduction in size at a low cost.

Japanese Patent Application Laid-Open No. 2002-170649

However, in the conventional configuration, the number of photocouplers corresponding to the number of temperature detection elements is required, which increases the number of components, resulting in an increase in cost and component mounting area.

SUMMARY OF THE INVENTION An object of the present invention is to provide a technique capable of preventing damage to an apparatus with a low-cost configuration without increasing the number of configurations for transmitting an abnormality of a heater more than necessary in a configuration having a plurality of temperature detection elements. is.

In order to achieve the above object, the image forming apparatus of the present invention includes:
a heater having a plurality of heat generating blocks that generate heat when energized;
a relay or switching means provided in a power supply path to the heater;
a plurality of triacs provided in power supply paths of the plurality of heat generating blocks ;
a driving unit that drives the plurality of triacs;
a plurality of temperature detection means arranged at a first potential for detecting the temperature of each of the plurality of heat generating blocks ;
a control unit arranged at a second potential insulated from the first potential and configured to control the drive unit based on the temperatures detected by the plurality of temperature detection means;
a plurality of abnormality detection circuit units arranged at the first potential and outputting signals corresponding to temperatures detected by the plurality of temperature detection means;
an abnormality transmission circuit unit that transmits an abnormality of the heater to the relay or switching means based on a signal output from the abnormality detection circuit unit;
An image forming apparatus that fixes an unfixed toner image formed on a recording material to the recording material by heat of the heater and outputs the image,
said relay or switching means being placed at said second potential;
The abnormality transmission circuit unit has an insulated communication means,
The plurality of abnormality detection circuit units are OR-connected to the abnormality transmission circuit unit,
The abnormality transmission circuit section is characterized by transmitting the signal after the OR connection to the relay or the switching means via the insulating communication means.

According to the present invention, in a configuration having a plurality of temperature detection elements, it is possible to prevent damage to the device with an inexpensive configuration without increasing the configuration for transmitting abnormality of the heater more than necessary.

Schematic cross-sectional views of image forming apparatuses of Examples 1 to 3 Schematic cross-sectional views of fixing devices of Examples 1 and 2 Heater Configuration Diagram of Fixing Device of Examples 1 and 2 Circuit diagram for power supply to fixing device of embodiment 1 Circuit diagram for power supply to fixing device of embodiment 1 Circuit diagram for power supply to fixing device of embodiment 1 Power Supply Circuit Diagram of Fixing Device of Embodiment 2 Power Supply Circuit Diagram of Fixing Device of Embodiment 2 Power Supply Circuit Diagram of Fixing Device of Embodiment 2 Schematic cross-sectional view of a fixing device of Example 3 Heater Configuration Diagram of Fixing Device of Embodiment 3 Power Supply Circuit Diagram for Fixing Device of Embodiment 3 Power Supply Circuit Diagram for Fixing Device of Embodiment 3 Power Supply Circuit Diagram for Fixing Device of Embodiment 3 Power Supply Circuit Diagram for Fixing Device of Embodiment 4 Power Supply Circuit Diagram for Fixing Device of Embodiment 4 Power Supply Circuit Diagram for Fixing Device of Embodiment 5

BEST MODE FOR CARRYING OUT THE INVENTION A mode for carrying out the present invention will be exemplarily described in detail below based on an embodiment with reference to the drawings. However, the dimensions, materials, shapes and relative arrangement of the components described in this embodiment should be appropriately changed according to the configuration of the device to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

[Example 1]
In the image forming apparatus 10 according to the first embodiment of the present invention, a heating element (resistive heating element) 302 and thermistors T1 to T4 are all arranged on the primary side, and a fixing device 200 as an image heating device is provided on the secondary side. By not arranging the elements, it is possible to reduce the size by eliminating the need to keep a safe distance. In such a configuration, outputs of abnormality detection circuits a to d based on temperature information of a plurality of thermistors T1 to T4 for detecting the temperature of the heating element 302 are OR-connected to the abnormality transmission means 408 or 409. FIG. Then, the power supply to the heating element 302 is stopped when any one of the abnormality detection circuits a to d operates. The above is the characteristic configuration of this embodiment.

[Configuration of Image Forming Apparatus]
FIG. 1 is a schematic diagram showing an example of an electrophotographic laser beam printer as an image forming apparatus according to the present embodiment. Here, an image forming operation in the image forming apparatus 10 will be described. Paper P as a recording material is fed one by one from a paper feed tray 11 by a paper feed roller 12 and is transported to a process cartridge 14 by a transport roller 13 at a predetermined timing. The process cartridge 14 incorporates a photosensitive drum 15 as an image carrier, charging means 16 and developing means 17 . A charging unit 16 is arranged in pressure contact with the photosensitive drum 15 , and the charging unit 16 uniformly charges the surface of the photosensitive drum 15 . After that, the scanner unit 19 serving as exposure means performs exposure based on image information to form an electrostatic latent image on the surface of the photosensitive drum 15 . Developing means 17 is provided downstream of the exposure position in the rotational direction of the photosensitive drum 15 . When the electrostatic latent image formed on the photosensitive drum 15 reaches a position facing the developing means 17 , toner is supplied from the developing means 17 to the electrostatic latent image, and a toner image (visible image) is formed on the photosensitive drum 15 . It is formed.

On the other hand, the paper P is transported at a timing synchronous with the moving speed of the toner image formed on the photosensitive drum 15, and the paper P that reaches the photosensitive drum 15 is subjected to transfer, which is the pressure contact portion between the photosensitive drum 15 and the transfer roller 20. At the nip, the toner image on the photosensitive drum 15 is transferred. After that, the paper P having the toner image transferred thereon is conveyed to a fixing device 200 as a fixing section having a heating element. The fixing device 200 includes two rollers that face and press against each other, and fixes the toner image on the paper P by heat and pressure. Electric power is supplied to the fixing device 200 from a power supply unit 24 connected to a commercial AC power source 25, thereby heating the heating element inside the fixing device 200. FIG. After that, the paper P is discharged out of the machine by paper discharge rollers 22 and 23, and a series of printing operations is completed. A cleaning unit 18 cleans the photosensitive drum 15 .

Note that the image forming apparatus is not limited to the one illustrated in FIG. 1, and may be, for example, an image forming apparatus having a plurality of image forming units. Furthermore, the image forming apparatus may include a primary transfer section for transferring the toner image on the photosensitive drum 15 to the intermediate transfer belt, and a secondary transfer section for transferring the toner image on the intermediate transfer belt to a sheet.

FIG. 2 is a schematic cross-sectional view of the fixing device 200 in this embodiment. The fixing device 200 includes a cylindrical film (endless belt) 202 , a heater 300 that contacts the inner surface of the film 202 , and a pressure roller (nip forming member) that forms a fixing nip portion N together with the heater 300 via the film 202 . ) 208 and . The material of the base layer of the film 202 is heat-resistant resin such as polyimide, or metal such as stainless steel. Also, an elastic layer such as heat-resistant rubber may be provided on the surface layer of the film 202 . The pressure roller 208 has a metal core 209 made of iron, aluminum or the like, and an elastic layer 210 made of silicone rubber or the like. The heater 300 is held by a holding member 201 made of heat-resistant resin. The holding member 201 also has a guide function of guiding the rotation of the film 202 . The pressure roller 208 receives power from a motor (not shown) as a power source and rotates in the direction of the arrow. The rotation of the pressure roller 208 causes the film 202 to rotate. The paper P carrying the unfixed toner image is heated while being nipped and conveyed in the fixing nip portion N to be fixed.

The heater 300 is a heater that is heated by heating elements 302 (302a, 302b) provided on the surface of a ceramic substrate 305 opposite to the side that contacts the holding member 201 (this surface is hereinafter defined as the surface). be. On the surface of the ceramic substrate 305 of the ceramic heater 300, thermistors T1, T2, T3, and T4, which are temperature detecting means, are in contact, and other temperature protection elements such as thermoswitches (not shown) are in contact. there is The thermistors T1 to T4 are temperature detecting elements, and are not limited to contact-type thermistors.

In this embodiment, the heating element 302 and thermistors T1 to T4 as temperature detecting means are all arranged on the primary side (primary side circuit) of the transformer 491 as the first potential side. A secondary side (secondary side circuit) element as the second potential side is not arranged. This eliminates the need to keep a safe distance and reduces the size.

A metal stay 204 applies a spring pressure (not shown) to the holding member 201 . Although the fixing device 200 in this embodiment is described as a ceramic heater, it is not limited to this. For example, even in a fixing device using a halogen heater, the same effect as in the first embodiment can be obtained.

FIG. 3 is a schematic diagram illustrating the configuration of the heater 300 of Example 1. FIG. FIG. 3A is a schematic cross-sectional view of the heater 300 near X0, which is the transport reference position shown in FIG. . The heater 300 has heating elements 302 a and 302 b provided along the longitudinal direction of the heater 300 on the surface of the sliding surface layer 1 that is the first surface on the substrate 305 . The heating element 302a is arranged on the upstream side in the conveying direction of the recording paper P, and the conductor 301b is arranged on the downstream side. A protective glass 307 covers the heating elements 302a and 302b.

FIG. 3B is a schematic plan view of the heater 300 of Example 1. FIG. The heat generating elements 302a and 302b on the sliding surface layer 1 are arranged in parallel along the longitudinal direction to form heat generating regions X1-X2. The heating elements 302a, 302b are connected to the electrodes E1, E2 via conductors 301a, 301b, 301c. Power is supplied to the heater 300 via the electrodes E1 and E2. The surface protection layer 307 on the sliding surface layer 2 covers the area of the sliding surface layer 1 excluding the electrodes E1 and E2. T1, T2, T3, and T4 indicated by dotted lines indicate the thermistors T1 to T4 shown in FIG. In order to detect the temperature of the heater 300, thermistors T1 to T4 using a material (NTC in this embodiment) having a positive (PTC) or negative (NTC) high TCR characteristic are brought into contact. The thermistors T1 and T4 are placed at both longitudinal ends of the heat generating region X1-X2, the thermistor T2 is placed near the center of the heater 300 in the longitudinal direction, and the thermistor T3 is placed at a position corresponding to the end of the small-size paper during transport. there is

FIG. 4A shows a circuit diagram of a power supply circuit to the fixing device 200 of Example 1. FIG. The power supply circuit is a circuit that supplies power from the AC power source 25 to the heating element 302 inside the fixing device 200 and performs temperature control so that the heat generating element 302 reaches a predetermined temperature. The insulated ACDC converter 400 is a switching power supply circuit that supplies a stable voltage V1 from the AC power supply 25 to the secondary side circuit. The voltage V 1 is supplied to the CPU 1 , and the CPU 1 as a control unit arranged on the secondary side controls driving elements (not shown) of the laser printer 10 , the image forming process, and the temperature of the fixing device 200 . CPU2 is arranged on the primary side, monitors the temperature of the thermistor, and transmits temperature information to CPU1. CPU1 and CPU2 perform isolated communication via the isolated communication means 401 .

The protection circuit block 402 is a circuit that operates to stop power supply to the heating element 302 based on the TH1 to TH4 signals. Power is supplied from the AC power supply 25 connected to the laser printer 10 to the heating element 302 inside the heater 300 via the relay RL1, the relay RL2, and the triac Q1, so that the heating element 302 generates heat.

Next, the operation of relay RL1 will be described. 417 and 418 denote resistors, and 419 and 420 denote NPN transistors. Relay RL1 is controlled by an RL1_ON signal output from CPU1. When the RL1_ON signal is High, the NPN transistor 419 for driving the relay is turned on to turn on RL1, and when the RL1_ON signal is Low, the NPN transistor 419 is turned off to turn off RL1. Relay RL2 operates based on the RL2_ON signal output from CPU1. Detailed operation is omitted because it is similar to that of relay RL1.

Next, the triac driving circuit 421 as a driving section will be described. 414 to 416 are resistors, 422 is a phototriac coupler, and Q1 is a triac. Power control of the heating element 302 is performed by energizing/interrupting the triac Q1. The triac Q1 is controlled by the FUSER1 signal output from the CPU1. ) is taken. When the FUSER1 signal goes low, a current flows through the secondary side diode of the phototriac coupler 422, and the primary side triac of the phototriac coupler 422 operates. Then, a trigger current flows through the gate terminal of the triac Q1 through the resistor 414 or the resistor 415, turning the triac Q1 ON.

Next, temperature detection by thermistors T1 to T4 will be described. Vcc indicates a stable voltage based on DCL (direct current reactor). The temperature detected by the thermistor T1 is detected by the CPU 2 as a TH1 signal, which is a voltage obtained by dividing the voltage Vcc by the resistor 441 and T1. Further, the temperature detected by the thermistor TH2 is detected by the CPU 2 as a TH2 signal by the voltage division of the resistor 442 and T2. Similarly, the temperature detected by the thermistor TH3 is detected by the resistors R443 and T3, and the temperature detected by the thermistor TH4 is detected by the CPU 2 as TH3 and TH4 signals by the voltage division of the resistors 444 and T4.

FIG. 4B shows an example of the isolated communication portion between CPU1 and CPU2 of FIG. 4A. The insulating communication means 401 is composed of resistors 481 to 484 , photocouplers 485 and 486 . The temperature detected by the CPU 2 is output as a CLK_OUT1 signal and a DATA_OUT1 signal, and data is transmitted to the CPU 1 on the secondary side as a CLK_IN1 signal and a DATA_IN1 signal, respectively. The CLK_OUT1 signal, the DATA_OUT1 signal, the CLK_IN1 signal, and the DATA_IN1 signal are reinforced and insulated by the photocouplers 485 and 486 . FIG. 4B shows a two-wire unidirectional communication system, but other communication systems or bidirectional communication systems may be used. For example, I2C (Inter-Integrated Circuit) may be used. Alternatively, UART (Universal Asynchronous Receiver Transmitter), SPI (Serial Peripheral Interface), etc. may be used. Thus, the temperature information of the heater 300 detected at TH1 to TH4 is transmitted from the CPU2 to the CPU1, and the CPU1 controls the power supplied from the AC power supply 25 to the heating element 302 based on the temperature information. . In the internal processing of the CPU 1, based on the set temperature of the heater 300 and the temperature information of the thermistor, the electric power to be supplied is calculated by PI control, for example. Further, the control level of the phase angle (phase control) and wave number (wave number control) corresponding to the power to be supplied is converted, and the triac Q1 is controlled according to the control conditions.

FIG. 4C shows an example of the protection circuit block 402 of FIG. 4A. The protection circuit block 402 is composed of abnormality detection means a to d as an abnormality detection circuit section, protection circuits 403 and 404 . The protection circuit 403 is connected to the abnormality detection means a and c, and is composed of an abnormality transmission means 408 and a latch circuit 406 as an abnormality transmission circuit section. The protection circuit 404 is connected to the abnormality detection means b and the abnormality detection means d, and is composed of an abnormality transmission means 409 and a latch circuit 407 as an abnormality transmission circuit section.

The abnormality detection circuits a to d are circuits that operate based on the voltages of the TH1 to TH4 signals that change according to the temperatures of the thermistors T1 to T4. In the figure, Vref1 to Vref4 are preset abnormal voltage thresholds, Vr1 to Vr4 are latch operation thresholds of the latch circuits 406 and 407, and 431 to 438 are open collector type comparators. 441 and 442 are NPN transistors, 449 and 450 are photocouplers, 451 to 454 are diodes, 455 to 466 are resistors, and 475 and 476 are capacitors.

Next, the operation of the protection circuit 403 when normal will be described. Since the thermistor T1 in FIG. 4A has an NTC characteristic, when the temperature of the thermistor T1 is low, the resistance value of the thermistor T1 is high and the voltage level of the TH1 signal is high. The voltage level of TH1 is sufficiently higher than the preset abnormal voltage threshold Vref1 when power is supplied to the heating element 302 and temperature control by the CPU 1 is performed normally, so the output of the comparator 431 becomes an open collector. . Therefore, since the base terminal of the NPN transistor 441 becomes High, the NPN transistor 441 is turned ON. Since a current flows to the light emitting side of the photocoupler 449 via the resistor 457, the transistor on the light receiving side is also turned ON, and the positive terminal of the comparator 435 becomes High. Since the voltage of the + terminal of the comparator 435 is higher than the preset latch operation threshold Vr1, the output of the comparator 435 becomes an open collector.

Since V1 is sufficiently larger than the preset latch operation threshold Vr2 of the comparator 436 of the latch circuit 406, the + terminal of the comparator 436 becomes higher than the - terminal, and the output of the comparator 436 becomes an open collector. Therefore, diode 452 will be OFF and the RL1_OFF signal will not turn NPN transistor 419 OFF.

Next, the operation of the protection circuit 403 when the heating element 302 abnormally heats will be described. Since the thermistor T1 in FIG. 4A has an NTC characteristic, when the temperature of the thermistor T1 increases, the resistance value of the thermistor T1 decreases and the voltage level of the TH1 signal decreases. If power supply to the heating element 302 and temperature control by the CPU 1 are not performed normally, and the heating element 302 abnormally heats, the voltage level of TH1 becomes lower than the preset abnormal voltage threshold Vref1. The output of 431 becomes Low. Therefore, the base terminal of the NPN transistor 441 becomes Low, and the NPN transistor 441 becomes OFF. Since no current flows to the light-emitting side of the photocoupler 449, the transistor on the light-receiving side is also turned off, and the positive terminal of the comparator 435 becomes Low. Since the voltage of the + terminal of the comparator 435 is lower than the preset abnormal voltage threshold Vr1, the output of the comparator becomes Low, and the RL1_OFF signal is made Low through the diode 452. As shown in FIG. 4A, when the RL1_OFF signal becomes Low, the NPN transistor 419 for driving the relay RL1 is turned OFF regardless of the RL1_ON signal, and the relay RL1 is also turned OFF. Therefore, power supply from the AC power source 25 to the heating element 302 can be turned off.

Further, when the output of the comparator 435 becomes Low, the voltage of the + terminal of the comparator 436 also becomes Low via the resistor 460 . Since the + terminal of the comparator 436 is lower than the preset latch operation threshold Vr2 of the comparator 436 of the latch circuit 406, the output of the comparator 436 becomes Low. Thereby, the power supply to the heating element 302 can be kept stopped until the power supply (not shown) of the comparator 436 is reset.

Since the operation of the abnormality detection means b, c, and d is the same as that of the abnormality detection means a, the explanation thereof is omitted. In addition, a protection circuit 404 independent of the protection circuit 403 is provided in order to secure the function as a protection means even in the event of a hardware failure typified by the failure of the protection circuit 403 or the NPN transistor 419 . ing. Since the operation of the protection circuit 404 is the same as that of the protection circuit 403, the description thereof is omitted.

The protection circuit block 402 may stop the power supply to the heating element 302 when an abnormality is detected in any one of the thermistors TH1 to TH4. Therefore, there is no need to specify which thermistor is faulty. Therefore, as shown in FIGS. 4A and 4C, by OR-connecting the abnormality detection means a and the abnormality detection means c to the abnormality transmission means 408, when any one of the abnormality detection means detects an abnormality, Power supply to the heating element 302 can be stopped.

As described above, by OR-connecting the output of the abnormality detection circuit to the abnormality transmission means, it is possible to secure the function as necessary protection means without increasing the number of the abnormality transmission means and latch circuits to the number of thermistors.

[Example 2]
A second embodiment of the present invention will be described. In the second embodiment, the CPU 3 that controls the driving of the laser printer 10 and the image forming process and the thermistors T1 to T4 are arranged on the secondary side, and the power supply to the heating element 302 is controlled based on the temperature information of the thermistors T1 to T4. The CPU 4 is arranged on the primary side. Among the configurations of the second embodiment, the configurations similar to those of the first embodiment are denoted by the same reference numerals, and descriptions thereof are omitted. In the second embodiment, matters that are not particularly described here are the same as in the first embodiment.

In the configuration of this embodiment, the switching means (RL1, RL2, Q1) for turning on/off the power supply to the heating element 302 and the CPU 4 for temperature control are arranged on the primary side. By doing so, it is possible to reduce the size of the device more inexpensively than in the first embodiment, since it is not necessary to provide double insulation for the switching means. In such a configuration, the outputs of the abnormality detection means eh based on the temperature information of the plurality of thermistors T1 to T4 for detecting the temperature of the heating element 302 are OR-connected to the abnormality transmission means 508 or 509. FIG. By doing so, it is possible to stop the power supply to the heating element 302 when any one of the abnormality detection means eh detects an abnormality.

Next, a second embodiment in which the heater 300 is mounted on the laser printer 10 will be described. A cross-sectional view of the fixing device 200 and a cross-sectional view of the heater 300 are the same as those in the first embodiment, and description thereof will be omitted. This embodiment differs from the first embodiment in that thermistors T1 to T4 are arranged on the secondary side. Further, in this embodiment, by covering the heating elements 302a and 302b with the surface protective layer 307 and the substrate 305 on the surface side of the heater 300, the heating elements 302a and 302b on the primary side of the AC power supply 25, the film 202, and the thermistor T1 are covered. ~T4 is double insulated. As means for obtaining double insulation, a method of obtaining double insulation by interposing an insulating member between the thermistors TH1 to TH4 and the heater 300 may be used.

FIG. 5A shows a circuit diagram of a power supply circuit to the fixing device 200 of the second embodiment. The power supply circuit is a circuit that supplies power from the AC power source 25 to the heating element 302 inside the fixing device 200 and controls the heating element 302 to reach a predetermined temperature. The secondary side voltage V1 is supplied to the CPU 3, and the CPU 3 arranged on the secondary side controls drive elements (not shown) of the laser printer 10 and the image forming process. The CPU 3 also monitors the temperatures of the thermistors T1-T4 based on the TH1-TH4 signals. The CPU 4 is arranged on the primary side and controls the power of the switching means (RL1, RL2, Q1) based on the thermistor temperature information obtained from the CPU 3 through the insulating communication means 510 . The protection circuit block 502 is a circuit that stops power supply to the heating element 302 based on the TH1 to TH4 signals.

Power is supplied from the AC power supply 25 connected to the laser printer 10 to the heating element 302 inside the heater 300 via the relays RL1, RL2, and the triac Q1, so that the heating element 602 generates heat. The operations of the relay RL1, the relay RL2 and the triac Q1 are the same as those of the first embodiment, so the description thereof is omitted.

In addition, in this embodiment, both the relay RL1, which is an element that energizes/cuts off the power supply to the heating element 302, and the CPU4 that controls the relay RL1 are on the primary side. No need to insulate. Therefore, the means for turning ON/OFF the heating element 302 is not limited to a relay, and a switching means such as a semiconductor may be used to turn on/off the current. Similarly, the relay RL2 and the triac Q1 may be configured without double insulation. Thus, in this embodiment, the circuit can be configured by replacing the switching element for controlling the power supply to the heating element 302 with an inexpensive semiconductor.

Next, temperature detection by thermistors T1 to T4 will be described. The temperature detected by the thermistor T1 is detected by the CPU 3 as a TH1 signal, which is a voltage obtained by dividing the voltage V1 by the resistor 441 and T1. Further, the temperature detected by the thermistor TH2 is detected by the CPU 3 as a TH2 signal by the voltage division of the resistor 442 and T2. Similarly, the temperature detected by the thermistor TH3 is detected by the resistors R443 and T3, and the temperature detected by the thermistor TH4 is detected by the CPU 3 as TH2, TH3, and TH4 signals by the voltage division of the resistors 444 and T4, respectively.

FIG. 5B shows an example of the isolation communication means 510 of FIG. 5A. The isolated communication means 510 is composed of resistors 581 to 584 , photocouplers 585 and 586 . The temperature detected by the CPU 3 is output as a CLK_OUT2 signal and a DATA_OUT2 signal, and data is transmitted to the CPU 4 on the primary side as a CLK_IN2 signal and a DATA_IN2 signal, respectively. The CLK_OUT2 signal, the DATA_OUT2 signal, the CLK_IN2 signal, and the DATA_IN2 signal are reinforced and insulated by the photocouplers 585 and 586 .

Thus, the temperature information of the heater 300 detected at TH1 to TH4 is transmitted from the CPU3 to the CPU4, and the CPU4 controls the power supplied from the AC power supply 25 to the heater 300 based on the temperature information of the heater 300. Is going. In the internal processing of the CPU 4, based on the set temperature of the heater 300 and the detected temperature of the thermistor, the electric power to be supplied is calculated by PI control, for example. Further, the control level of the phase angle (phase control) and wave number (wave number control) corresponding to the power to be supplied is converted, and the triac Q1 is controlled according to the control conditions.

FIG. 5C shows an example of the protection circuit block 502 of FIG. 5A. The protection circuit block 502 is composed of abnormality detection means e to h, a protection circuit 503 and a protection circuit 504 . The protection circuit 503 is composed of an abnormality transmission means 508 and a latch circuit 506 to which the abnormality detection means e and the abnormality detection means g are connected. The protection circuit 504 is connected to the abnormality detection means f and h, and is composed of an abnormality transmission means 509 and a latch circuit 507 . The abnormality detection circuits e to h are circuits that operate based on the voltages of the TH1 to TH4 signals that change according to the temperatures of the thermistors T1 to T4. In the figure, 531 to 536 are open collector type comparators, 541 to 546 are Nch type MOSFETs, and 547 and 548 are NPN type transistors. 549 and 550 are photocouplers, 551 and 552 are diodes, 555 to 574 are resistors, and 575 and 576 are capacitors.

Next, the operation of the protection circuit 503 when normal will be described. Since the thermistor T1 in FIG. 5A has an NTC characteristic, when the temperature of T1 is low, the resistance value of T1 is high and the voltage level of the TH1 signal is high. The voltage level of TH1 is sufficiently higher than the preset abnormal voltage threshold Vref1 when power is supplied to heating element 302 and temperature control is performed normally by CPU3 and CPU4, so the output of comparator 531 is Low. Become. Therefore, since the gate terminal of the MOSFET 541 becomes Low, the MOSFET 541 becomes OFF. Since the MOSFET 545 is turned on and a voltage is supplied to the light emitting side of the photocoupler 549 , the transistor on the light receiving side is also turned on and current flows through the resistor 558 to the light receiving side. Since the base-emitter voltage of the NPN transistor 547 becomes Low, the NPN transistor 547 is turned off.

Also, since the voltage V1 is sufficiently higher than the latch operation threshold value Vr2 of the comparator 535 of the latch circuit 506, the + terminal of the comparator 535 becomes higher than the - terminal, and the output of the comparator 535 becomes an open collector. Therefore, the RL1_OFF signal does not turn off NPN transistor 419 .

Also, since the SAFE1 signal is input to the CPU 3, the CPU 3 can detect whether the abnormality detection circuit e or the abnormality detection circuit g is operating. When normal, the CPU 3 detects the SAFE1 signal as a Low signal. Similarly, the SAFE2 signal can detect whether fault detection circuit f or fault detection circuit h is operating.

Next, the operation of the protection circuit 503 when the heating element 302 abnormally heats will be described. Since the thermistor T1 in FIG. 5A has an NTC characteristic, when the temperature of the thermistor T1 increases, the resistance value of the thermistor T1 decreases and the voltage level of the TH1 signal decreases. As shown in FIG. 5C, when power supply to the heating element 302 and temperature control by the CPU3 and CPU4 are not performed normally, the heating element 302 generates abnormal heat, and the voltage level of TH1 is set in advance. It becomes lower than the abnormal voltage threshold Vref1. Therefore, the output of the comparator 531 becomes an open collector. Therefore, a current flows through the gate terminal of the MOSFET 541 via the resistor 555, so that the MOSFET 541 is turned ON. Since the drain voltage of MOSFET 541 becomes Low, MOSFET 545 is turned OFF. Since no voltage is supplied to the light emitting side of the photocoupler 549, the transistor on the light receiving side is turned off. Since the base voltage of the NPN transistor 547 becomes High, the NPN transistor 547 is turned ON and the RL1_OFF signal is made Low. As shown in FIG. 5A, when the RL1_OFF signal becomes Low, the NPN transistor 419 for driving the relay RL1 is turned OFF regardless of the RL1_ON signal, and the relay RL1 is also turned OFF. Therefore, power supply from the AC power source 25 to the heating element 302 can be turned off.

Moreover, when the MOSFET 541 is turned ON, the voltage of the + terminal of the comparator 535 also becomes Low via the resistor 563 . Since the + terminal of the comparator 535 is lower than the preset latch operation threshold Vr2 of the comparator 535 of the latch circuit 506, the output of the comparator 535 becomes Low. Thereby, the power supply to the heating element 302 can be kept stopped until the power supply (not shown) of the comparator 535 is reset.

Since the operation of the abnormality detection means f, g, and h is the same, the explanation is omitted. In addition, a protection circuit 504 independent of the protection circuit 503 is provided in order to ensure the function as a protection means even in the event of a hardware failure typified by the failure of the protection circuit 503 or the NPN transistor 419 . ing. Since the operation of the protection circuit 504 is the same as that of the protection circuit 503, description thereof will be omitted.

The protection circuit block 502 may stop the power supply to the heating element 302 when an abnormality is detected in any one of the thermistors TH1 to TH4. Therefore, there is no need to specify which thermistor is faulty. Therefore, as shown in FIGS. 5A and 5D, by OR-connecting the abnormality detection means e and the abnormality detection means g to the abnormality transmission means 508, any one of the abnormality detection means detects an abnormality. When this occurs, power supply to the heating element 302 can be stopped.

As described above, in this embodiment, the thermistor and the abnormality detection means are arranged on the secondary side, and the power control means is arranged on the primary side. Even in such a configuration, by OR-connecting the output of the abnormality detection circuit to the abnormality transmission means, it is possible to secure the necessary function as the protection means without increasing the number of the abnormality transmission means and latch circuits to the number of thermistors. .

[Example 3]
In the third embodiment of the present invention, the CPU 5 for controlling the driving of the laser printer 10, the image forming process, and the temperature control of the heating element 702 is arranged on the secondary side, and the switching means is arranged on the primary side. Further, thermistors T11, 21, 31, 41, 51, 61, 71, thermistors T12, 22, 32, 42, 52, 62, 72, and the CPU 6, which communicates temperature information of the thermistors with the CPU 5, are insulated from the primary and the secondary. placed at the intermediate potential. The above is the characteristic configuration of this embodiment. Among the configurations of the third embodiment, the same reference numerals are used for the same configurations as those of the above-described embodiments, and the description thereof is omitted. In Example 3, matters not specifically described here are the same as those in the above example.

In the configuration of this embodiment, the thermistors T11 to T71 and the thermistors T12 to T72 are insulated from both the primary circuit and the secondary circuit, and the surface protective layer is thinned, so that the thermal response of the heater 700 can be improved. . In such a configuration, the outputs of the plurality of thermistors T11 to T71 for detecting the temperature of the heating element 702, the abnormality detection circuits 1a to 1f based on the temperature information of the thermistors T12 to T72, and the outputs of the abnormality detection circuits 2a to 2g are transmitted to the abnormality transmission means 808. Alternatively, it is OR-connected to the abnormality transmission means 809 . By doing so, the power supply to the heating element 702 can be stopped when any one of the abnormality detection circuits operates.

Next, a third embodiment in which a fixing device 600 and a heater 700 are mounted on the laser printer 10 will be described. The same symbols are used for the same configurations as those of the first and second embodiments, and the description thereof is omitted. The laser printer 10 of this embodiment is compatible with a plurality of recording material sizes. Letter paper (approximately 216 mm×279 mm), Legal paper (approximately 216 mm×356 mm), and A4 paper (210 mm×297 mm) can be set in the paper feed cassette 11 . Furthermore, Executive paper (about 184 mm x 267 mm), JIS B5 paper (182 mm x 257 mm), and A5 paper (148 mm x 210 mm) can also be set. The printer of this example is basically a laser printer that feeds paper longitudinally (conveys the paper so that the long side is parallel to the conveying direction). Note that the configuration of this proposal can be similarly applied to a printer that horizontally feeds paper. Of the widths of standard recording materials (widths of recording materials in the catalog) supported by the apparatus, the recording materials having the largest width are Letter paper and Legal paper. is approximately 216 mm. In this embodiment, a recording material P having a paper width smaller than the maximum size supported by the apparatus is defined as small size paper.

The heater 700 of the third embodiment has a configuration in which the heating blocks HB1 to HB7 can be independently controlled, unlike the heaters 300 of the first and second embodiments. By controlling the temperature of the heat generating blocks HB1 to HB7 based on the recording material size and image information, it is possible to suppress the temperature rise in non-sheet-passing areas when small-size sheets are passed through, and to reduce heat generation in areas that do not require heating. By reducing it, the power consumption of the fixing device 600 can be reduced.

FIG. 6 is a schematic cross-sectional view of a fixing device 600 of Example 3. As shown in FIG. The fixing device 600 has an electrode (the electrode E34 is shown here as a representative) provided on the opposite side of the fixing nip portion N, and a plurality of electrical contacts (not shown). is supplying power to A detailed description of heater 700 is provided in FIG.

The heater 700 is a heater that is heated by heating elements 702 (702a, 702b) provided on the back surface side of the substrate 705 . A surface protective layer 707 is glass used to insulate the heating element 702 . A thermistor T41 (T11 to T71 and T12 to T72) is provided on the sliding surface side of the substrate 705. As shown in FIG. The surface protective layer 708 is glass used to protect the thermistor T41 (T11 to T71 and T12 to T72) and to obtain the slidability of the fixing nip portion N. FIG. The holding member 201 of the heater 700 and the surface protective layer 707 are provided with holes for connecting electrodes and electrical contacts. A detailed description will be given with reference to FIG.

FIG. 7 is a schematic diagram illustrating the configuration of a heater 700 according to the third embodiment. FIG. 7A shows a cross-sectional view near the transport reference position X0 shown in FIG. 7B in the short direction of the heater 700 (the transport direction of the recording material P). The heater 700 has a first conductor 701 and a second conductor 703 provided on a substrate 705 along the longitudinal direction of the heater 700 . The first conductors 701 (701a, 701b) and the second conductors 703 (703-4) are provided along the longitudinal direction of the heater 700 at different positions on the substrate 705 in the lateral direction of the heater 700. ing. The first conductor 701 is separated into a conductor 701a arranged on the upstream side in the conveying direction of the recording material P and a conductor 701b arranged on the downstream side.

The heating element 702 is provided between the first conductor 701 and the second conductor 703 and generates heat by electric power supplied through the first conductor 701 and the second conductor 703 . The heating element 702 is separated into a heating element 702a arranged on the upstream side in the conveying direction of the recording material P and a heating element 702b arranged on the downstream side. If the heat generation distribution in the width direction of the heater 700 becomes asymmetrical, the stress generated in the substrate 705 when the heater 700 generates heat increases. When the stress generated in the substrate 705 increases, the substrate 705 may crack. Therefore, the heating element 702 is separated into a heating element 702a arranged on the upstream side in the conveying direction and a heating element 702b arranged on the downstream side so that the heat generation distribution in the width direction of the heater 700 is symmetrical. . In addition, the back layer 2 of the heater 700 has an insulating (glass in this embodiment) covering the heating element 702, the first conductors 701 (701a, 701b) and the second conductors 703 (703-4). A surface protective layer 707 is provided to avoid the electrode portion (E34).

A plan view of each layer of heater 700 is shown in FIG. 7B. Heater 700 back layer 1 is provided with a plurality of heat generating blocks each including a set of first conductor 701 , second conductor 703 and heat generating element 702 in the longitudinal direction of heater 700 . The heater 700 of this embodiment has a total of seven heat generating blocks HB1 to HB7 at the central portion and both ends of the heater 700 in the longitudinal direction. The heat generating blocks HB1 to HB7 are composed of heat generating elements 702a-1 to 702a-7 and heat generating elements 702b-1 to 702b-7, which are formed symmetrically in the width direction of the heater 700, respectively. The first conductor 701 is composed of a conductor 701a connected to the heating elements (702a-1 to 702a-7) and a conductor 701b connecting to the heating elements (702b-1 to 702b-7). Similarly, the second conductor 703 is divided into seven conductors 703-1 to 703-7 to correspond to the seven heat generating blocks HB1 to HB7.

Electrodes E31 to E37 are electrodes used to supply electric power to the heating blocks HB1 to HB7 via conductors 703-1 to 703-7, respectively. The electrodes E38 and E39 are electrodes used for connecting to a common electrical contact used for power feeding to the seven heating blocks HB1 to HB7 via the conductors 701a and 701b.

Also, the surface protective layer 707 of the back layer 2 of the heater 700 is formed except for the electrodes E31 to E39, so that an electrical contact (not shown) can be connected from the back side of the heater 700. FIG. Then, power can be supplied to each heat generating block independently, and power supply control can be performed independently. By dividing into seven heating blocks in this manner, four paper passing areas such as AREA1 to AREA4 can be formed. In this embodiment, AREA1 is classified as A5 paper, AREA2 is classified as B5 paper, AREA3 is classified as A4 paper, and AREA4 is classified as Letter paper. Since the seven heat generating blocks can be controlled independently, the heat generating blocks to be supplied with power are selected according to the size of the recording paper P. The number of heat generating regions and the number of heat generating blocks are not limited to those in this embodiment. Moreover, the heating elements 702a-1 to 702a-7 and 702b-1 to 702b-7 in each heating block are not limited to a continuous pattern as described in this embodiment, and are provided with gaps. A strip-shaped pattern may also be used.

By providing an electrode on the back surface of the heater 700 in this way, it is not necessary to perform wiring by means of a conductive pattern on the substrate 705, so that the width of the substrate 705 in the lateral direction can be reduced. Therefore, it is possible to obtain the effect of reducing the material cost of the substrate 705 and shortening the start-up time required for the temperature rise of the heater 700 due to the reduction of the heat capacity of the substrate 705 .

Thermistors T11 to T71 and thermistors T12 to T72 are installed on the sliding surface layer 1 of the heater 700 in order to detect the temperature of each of the heating blocks HB1 to HB7 of the heater 700 . Since each of the heat generating blocks HB1 to HB7 has two or more thermistors, even if one thermistor fails, the temperature of all the heat generating blocks can be detected. In order to energize the thermistors T11 to T71 and the thermistors T12 to T72, conductors ET1-1 to ET7-1 and conductors ET1-2 to ET7-2 for detecting the resistance values of the thermistors, and a common conductor EG9 for the thermistors are provided. , EG10 are formed.

The sliding surface layer 2 of the heater 700 (the surface in contact with the endless belt) has a surface protective layer 708 made of a slidable glass coating. The surface protective layer 708 provides electrical contacts to the conductors ET1-1 to ET7-1, the conductors ET1-2 to ET7-2, and the conductors EG9 and EG10 for detecting the resistance value of the thermistor. , are provided at least in the region where the film 202 slides.

Thus, in this embodiment, by covering the heating element 702 with the surface protective layer 707 and the substrate 705 of the heater 700, the heating element 702 on the primary side, the film 202, the thermistors T11 to T71, and the thermistors T12 to T72 insulated between The protection circuit block 802 and the CPU 6 are insulated from both the primary side and the secondary side. That is, since the thermistors T11 to T71 and the thermistors T12 to T72 are insulated from both the primary side and the secondary side, the surface protection layer 708 can be made thin. Insulation is ensured by the surface protective layer 708, so the thermistors T11 to T71, T12 to T72, and the conductors ET1-1 to ET7-1, ET1-2 to ET7-2, EG9, and EG10 connecting the thermistors are , can be placed at any position on the substrate 705 sliding surface layer. Therefore, the substrate width of the heater 700 in the lateral direction can be shortened, and the thermal responsiveness of the heater 700 can be improved.

Therefore, by using the heater 700 of the third embodiment and the power supply circuit described with reference to FIG. Can improve accuracy.

FIG. 8A shows a circuit diagram of a power supply circuit to the fixing device 600 of the third embodiment. The power supply circuit is a circuit that supplies power from the AC power source 25 to the heating element 702 inside the fixing device 600 and controls the heating element 702 to reach a predetermined temperature. The voltage V1 generated by the insulated AC/DC converter 400 is supplied to the CPU 5, and the CPU 5 arranged on the secondary side controls drive elements (not shown) of the laser printer 10 and the image forming process. T11-T71, T12-T72, their peripheral circuits, abnormality detection means 1a-1g, 2a-2g, and CPU 6 are placed at an intermediate potential insulated from both the primary and secondary sides.

Next, the operation of generating the voltage V2 by the transformer 889 will be described. A transformer 889 is an insulating transformer used to generate the voltage V2 from the secondary voltage V1, and is insulated. A voltage is output by switching the Nch-type MOSFET 890 according to the TR_CLK signal of the CPU 5 . A diode 891 and a capacitor 892 rectify and smooth the output of the transformer 889 to generate a stable voltage V2.

The isolated communication means 810 is an isolated communication circuit between the CPU5 and the CPU6. The CPU 5 is arranged on the secondary side and controls the power of the switching means (RL1, RL2, Q1 to Q7) based on the thermistor temperature information obtained from the CPU 6 by the insulating communication means 810 .

The protection circuit block 802 is a circuit that stops power supply to the heating element 702 based on the TH11 to TH71 signals and the TH12 to TH72 signals.

Power is supplied from the AC power supply 25 connected to the laser printer 10 to the heating element 702 inside the heater 700 through the relays RL1 and RL2 and the triacs Q1 to Q7, thereby heating the heating element 702 (702a-1, 702b- 1) generates heat. When heating elements 702a-1 and 702b-1 generate heat, relay RL1, relay RL2 and triac Q1 are operated. Further, when the other heating elements 702-2 to 702-7 are to be heated, the triacs Q2 to Q7 are operated respectively. The operations of the relay RL1, the relay RL2, and the triacs Q1 to Q7 are the same as those of the first embodiment, so the description thereof is omitted.

Next, temperature detection by the thermistors T11 to T71 and the thermistors T12 to T72 will be described. The temperature detected by the thermistor T11 is detected by the CPU 6 as a TH11 signal, which is a voltage obtained by dividing the voltage V2 by the resistor 811 and T11. Similarly, the temperature detected by thermistor T21 is detected by CPU 6 as a TH21 signal due to the voltage division of resistor 812 and T12. The temperature detected by the thermistor T31 is detected by the CPU 6 as a TH31 signal by dividing the voltage of the resistor 813 and T13. The temperature detected by thermistor T41 is detected by CPU 6 as a TH41 signal due to the voltage division of resistor 814 and T14. The temperature detected by the thermistor T51 is detected by the CPU 6 as a TH51 signal by dividing the voltage of the resistor 815 and T15. The temperature detected by thermistor T61 is detected by CPU 6 as a TH61 signal due to the voltage division of resistor 816 and T16. The temperature detected by thermistor T71 is detected by CPU 6 as a TH71 signal due to the voltage division of resistor 817 and T17. The temperature detected by the thermistor T12 is detected by the CPU 6 as a TH12 signal by dividing the voltage of the resistor 821 and T21. The temperature detected by thermistor T22 is detected by CPU 6 as a TH22 signal due to the voltage division of resistor 822 and T22. The temperature detected by the thermistor T32 is detected by the CPU 6 as a TH32 signal by dividing the voltage of the resistor 823 and T32. The temperature detected by thermistor T42 is detected by CPU 6 as a TH42 signal by the voltage divider of resistor 824 and T42. The temperature detected by thermistor T52 is detected by CPU 6 as a TH52 signal due to the voltage division of resistor 825 and T52. The temperature sensed by thermistor T62 is sensed by CPU 6 as a TH62 signal by the voltage divider of resistor 826 and T62. The temperature detected by thermistor T72 is detected by CPU 6 as a TH72 signal due to the voltage division of resistor 827 and T72.

FIG. 8B is a circuit diagram showing an example of the isolation communication means 810 of FIG. 8A. The isolated communication means 810 is composed of resistors 830 to 833 , a photocoupler 834 and a photocoupler 835 . The temperature detected by the CPU 6 is output as a CLK_OUT3 signal and a DATA_OUT3 signal, and data is transmitted to the CPU 7 on the secondary side as a CLK_IN3 signal and a DATA_IN3 signal, respectively. The CLK_OUT3 signal, the DATA_OUT3 signal and the CLK_IN3 signal, the DATA_IN3 signal are insulated by the photocoupler 834 and the photocoupler 836 .

In this way, the temperature information of the heater 700 detected by TH11 to TH71 and TH12 to TH72 is transmitted from the CPU 6 to the CPU 5, and based on the temperature information of the heater 700, the CPU 5 supplies from the AC power supply 25 to the heater 700. It controls power. In the internal processing of the CPU 5, based on the set temperature of the heater 700 and the detected temperature of the thermistor, the electric power to be supplied is calculated by PI control, for example. Furthermore, the phase angle (phase control) and wave number (wave number control) corresponding to the power to be supplied are converted into control levels, and the triac Q
1 to Q7 are controlled.

FIG. 8C shows an example of the protection circuit block 802 of FIG. 8A. The protection circuit block 802 is composed of abnormality detection means 1a to 1g and abnormality detection means 2a to 2g, a pulse detection circuit 805, a protection circuit 803, and a protection circuit 804. FIG. The protection circuit 803 is connected to the abnormality detection means 1a to 1g, and is composed of an abnormality transmission means 808 and a latch circuit 806. FIG. The protection circuit 804 is connected to the abnormality detection means 2a to 2g, and is composed of an abnormality transmission means 809 and a latch circuit 807. FIG.

The abnormality detection circuits 1a to 1g are circuits that operate based on the voltages of the TH11 to TH71 signals that change according to the temperatures of the thermistors T11 to T71. In the figure, Vref11 to Vref71 and Vref12 to Vref71 are preset abnormal voltage thresholds, and 840 to 842 are open collector type comparators. 843 to 848 are resistors, 849 is a photocoupler, 850 and 851 are diodes, 852 is a capacitor, and 853 is an NPN transistor.

Next, the operation of the protection circuit 803 when normal will be described. Since the thermistor T11 in FIG. 8A has an NTC characteristic, when the temperature of T11 is low, the resistance value of T11 is high and the voltage level of the TH11 signal is high. The voltage level of TH11 is sufficiently higher than the preset abnormal voltage threshold Vref11 when power is supplied to the heating elements 702a-1 and 702b-1, temperature detection by the CPU 6, and temperature control by the CPU 5 are normally performed. . Therefore, the output of the comparator 840 becomes an open collector. Therefore, since the base terminal of the NPN transistor 853 becomes High, the NPN transistor 853 is turned ON. Since a current flows through the light emitting side of the photocoupler 849, the transistor on the light receiving side is also turned ON, and the positive terminal of the comparator 841 becomes High. Since the voltage of the + terminal of the comparator 841 is higher than the preset latch operation threshold Vr1, the output of the comparator 841 becomes an open collector.

Since V1 is sufficiently larger than the preset latch operation threshold value Vr2 of the comparator 842 of the latch circuit 806, the + terminal of the comparator 842 becomes higher than the - terminal, and the output of the comparator 842 becomes an open collector. Therefore, diode 851 will be OFF and the RL1_OFF signal will not turn NPN transistor 419 OFF.

Next, the operation of the protection circuit 803 when the heating element 702 abnormally heats will be described. Since the thermistor T11 in FIG. 8A has an NTC characteristic, when the temperature of the thermistor T11 increases, the resistance value of the thermistor T11 decreases and the voltage level of the TH11 signal decreases. When power supply to the heating elements 702a-1 and 702b-1, temperature detection by the CPU 6, and temperature control by the CPU 5 are not performed normally, the heating elements 702a-1 and 702b-1 may generate abnormal heat. In this case, the voltage level of TH11 becomes lower than the preset abnormal voltage threshold Vref11, so the output of comparator 840 becomes Low. Therefore, a current flows through the output terminal of the comparator 840 through the resistor 843, so that the NPN transistor 853 is turned off. Since no voltage is supplied to the light-emitting side of the photocoupler 846, the transistor on the light-receiving side is also turned off, and the + terminal of the comparator 841 becomes Low. Since the voltage at the + terminal of the comparator 841 is lower than the preset abnormal voltage threshold Vr1, the output of the comparator 841 becomes Low, and the RL1_OFF signal is made Low via the diode 851. As shown in FIG. 8A, when the RL1_OFF signal becomes Low, the NPN transistor 419 for driving the relay RL1 is turned OFF regardless of the RL1_ON signal, and the relay RL1 is also turned OFF. Therefore, power supply from the AC power supply 25 to the heating element 702 can be turned off.

Further, when the output of the comparator 841 becomes Low, the voltage of the + terminal of the comparator 842 also becomes Low via the resistor 847 . Since the + terminal of the comparator 842 is lower than the preset latch operation threshold Vr2 of the comparator 842 of the latch circuit 806, the output of the comparator 842 becomes Low. Thereby, the power supply to the heating element 702 can be kept stopped until the power supply (not shown) of the comparator 842 is reset.

Since the operation of the abnormality detection means 1b to 1g and the abnormality detection means 2a to 2g is the same as that of the abnormality detection circuit 1a, description thereof will be omitted. In addition, a protection circuit 804 independent of the protection circuit 803 is provided in order to secure the function as a protection means even in the event of a hardware failure typified by the failure of the protection circuit 803 or the NPN transistor 419 . ing. Since the operation of the protection circuit 804 is the same as that of the protection circuit 803, description thereof is omitted.

Next, the operation of pulse detection circuit 805 will be described. 870 to 873 are resistors, 874 and 875 are capacitors, 876 and 877 are diodes, 878 is an Nch MOSFET, and 879 is an NPN transistor. The CPU 6 outputs a predetermined pulse signal CPU_CLK when operating normally, and CPU_CLK is a fixed High (or Low) output when not operating normally.

A case where the CPU 6 is operating normally will be described. Since CPU_CLK is a pulse signal, CPU_CLK is AC-coupled by capacitor 874, rectified and smoothed by diodes 876, 877 and capacitor 875, and a high level voltage is applied to the gate terminal of MOSFET878. MOSFET 878 turns ON and current flows through resistor 872 . The base voltage of the NPN transistor 879 becomes Low, and the NPN transistor 879 is turned OFF. Therefore, the RL1_OFF signal does not turn off NPN transistor 419 .

Next, a case where the CPU 6 does not operate normally due to noise or the like will be described. Since the CPU_CLK signal goes high (or low), it is not carried by capacitor 874 and the gate voltage of MOSFET 878 goes low. MOSFET 878 is turned off, and voltage V 2 is applied to the base terminal of NPN transistor 879 through resistor 872 . The NPN transistor 879 turns ON, and the base of the NPN transistor 853 connected to the collector of the NPN transistor 879 becomes Low. When the base of NPN transistor 853 goes low, the RL1_OFF signal goes low, turning off relay RL1.

As described above, according to the pulse detection circuit 805, even when the CPU 6 does not operate normally due to noise or the like, power supply from the AC power supply 25 to the heating element 702 can be turned off. Even when the CPU 6 is operating normally, when the CPU 6 detects an abnormal temperature, CPU_CLK outputs High (or Low) to turn off the power supply from the AC power supply 25 to the heating element 702. can do.

In this embodiment, a heating element 602, a CPU 6, thermistors T11 to T71 and T12 to T72, and abnormality detection means 1a to 1g and 2a to 2g are arranged inside the fixing device 600. FIG. The fixing device 600 is normally detachable and connected to the laser printer 10 using a connector or the like. As in the present embodiment, the signal after the OR connection is arranged on the fixing device 600 side, and the latch circuit and the like after the OR connection are arranged on the laser printer side. and the number of pins required to connect the laser printer 10 can be reduced.

As shown in FIG. 8C, in this embodiment, V2 is used as the power supply on the light emitting side of the photocoupler 846, and the power supply from the AC power supply 25 to the heating element 702 can be turned off when the photocoupler 846 does not emit light. It is a configuration that can be used. With such a configuration, power supply from the AC power supply 25 to the heating element 702 can be turned off in the event of a predetermined abnormality. Examples of the abnormal state include when a component such as the MOSFET 890 fails and the voltage V2 is not output, or when a connector (not shown) is disconnected and the voltage V2 is not sent to the fixing device 600.

The protection circuit block 802 may stop power supply to the heating element 702 when detecting an abnormality in one of the thermistors T11 to T71 and T12 to T72. Therefore, there is no need to specify which thermistor is faulty. Therefore, as shown in FIGS. 8A and 8C, by OR-connecting the abnormality detection means 1a to 1g to the abnormality transmission means 808, when any one of the abnormality detection means detects an abnormality, the heating element 702 power supply to the Also, when the CPU 6 malfunctions due to noise or the like, the power supply from the AC power supply 25 to the heating element 702 can be turned off.

As described above, in the embodiment, the drive circuit of the power control means is arranged on the secondary side, and the thermistor and the abnormality detection means are arranged at potentials insulated from the primary side and the secondary side. The output of the circuit and the pulse detection circuit are OR'ed to the fault communication means. By doing so, it is possible to secure the function as necessary protection means without increasing the number of abnormality transmission means and latch circuits to the number of thermistors.

[Example 4]
In the fourth embodiment of the present invention, the contact side of the relay RL1 is connected to the AC power supply 25, the coil side of the relay RL1 and the NPN transistor 419 are connected to the intermediate potential V2, thereby turning off the relay without using an insulating element such as a photocoupler. It is characterized by being able to According to such a configuration, the protection circuit can be configured with a cheaper configuration. Among the configurations of the fourth embodiment, the same reference numerals are used for the same configurations as those of the above-described embodiments, and the description thereof is omitted. In Example 4, matters that are not particularly described here are the same as those in the above example.

A fourth embodiment in which a fixing device 600 and a heater 700 are mounted on the laser printer 10 will be described with reference to FIG. FIG. 9A is a circuit diagram of a power supply circuit to the fixing device 600 of the fourth embodiment. Unlike the third embodiment, the relay RL1 is placed between the primary side and the intermediate potential. Also, the protection circuit 903 is placed at an intermediate potential. FIG. 9B shows an example of the protection circuit block 902 of FIG. 9A. The protection circuit block 902 is composed of abnormality detection means 1 a to 1 g and abnormality detection means 2 a to 2 g, a pulse detection circuit 805 , a protection circuit 804 and a protection circuit 903 .

The operation of the protection circuit 903 when normal will be described. Since the thermistor T11 in FIG. 9A has an NTC characteristic, when the temperature of T11 is low, the resistance value of T11 is high and the voltage level of the TH11 signal is high. The voltage level of TH11 is sufficiently higher than the preset abnormal voltage threshold Vref11 when power is supplied to the heating elements 702a-1 and 702b-1, temperature detection by the CPU 6, and temperature control by the CPU 5 are normally performed. . Therefore, the output of the comparator 840 becomes an open collector. Since the voltage of the + terminal of the comparator 841 is higher than the preset latch operation threshold Vr1, the output of the comparator 841 becomes an open collector.

Also, since V2 is sufficiently larger than the preset latch operation threshold Vr2 of the comparator 842, the + terminal of the comparator 842 becomes higher than the - terminal, and the output of the comparator 842 becomes an open collector. Therefore, the diode 851 is turned OFF, and the RL1_OFF signal becomes HIGH through the resistor 851, so that the NPN transistor 419 is turned ON.

The operation of the protection circuit 903 when the heating element 702 abnormally generates heat will be described. Since the thermistor T11 in FIG. 9A has an NTC characteristic, when the temperature of the thermistor T11 increases, the resistance value of the thermistor T11 decreases and the voltage level of the TH11 signal decreases. When power supply to the heating elements 702a-1 and 702b-1, temperature detection by the CPU 6, and temperature control by the CPU 5 are not performed normally, the heating elements 702a-1 and 702b-1 may generate abnormal heat. In this case, the voltage level of TH11 becomes lower than the preset abnormal voltage threshold Vref11, so the output of comparator 840 becomes Low. Therefore, current flows through the output terminal of the comparator 840 through the resistor 843, and the + terminal of the comparator 841 becomes Low. Since the voltage at the + terminal of the comparator 841 is lower than the preset abnormal voltage threshold Vr1, the output of the comparator 841 becomes Low, and the RL1_OFF signal is made Low via the diode 851. As shown in FIG. 9A, when the RL1_OFF signal becomes Low, the NPN transistor 419 for driving the relay RL1 is turned OFF, and the relay RL1 is also turned OFF. Therefore, power supply from the AC power supply 25 to the heating element 702 can be turned off.

Further, when the output of the comparator 841 becomes Low, the voltage of the + terminal of the comparator 842 also becomes Low via the resistor 847 . Since the + terminal of the comparator 842 is lower than the preset latch operation threshold Vr2 of the comparator 842, the output of the comparator 842 becomes Low. Thereby, the power supply to the heating element 702 can be kept stopped until the power supply (not shown) of the comparator 842 is reset.

As described above, by arranging the abnormality detection circuit at the intermediate potential and arranging the relay so as to insulate between the primary side and the intermediate potential, it is not necessary to insulate the ON/OFF signals of the relay. , the protective means can be configured at low cost.

[Example 5]
Embodiment 5 of the present invention is characterized in that the coil side of relay RL1 is connected in series to GND (ground) via EG9 and EG10 of heater 700 and temperature protection element 1000 such as a thermoswitch. According to such a configuration, it is possible to configure the protection circuit with an inexpensive configuration. Among the configurations of the fifth embodiment, the same reference numerals are used for the same configurations as those of the above-described embodiments, and the description thereof is omitted. In Example 5, matters not specifically described here are the same as those in the above example.

A fifth embodiment in which a laser printer 10 is equipped with a fixing device 600 and a heater 700 will be described with reference to FIG. FIG. 10 is a circuit diagram of a power supply circuit to the fixing device 600 of the fifth embodiment.

The operation of relay RL1 when normal will be described. As shown in FIG. 10, the coil side of relay RL1 is connected to the collector terminal of NPN transistor 419, and the emitter terminal of NPN transistor 419 is connected to one end of conductor EG9 of heater 700. FIG. The other (other end) terminal of EG9 is connected to one end of EG10 on the short side of heater 700, and the other (other end) terminal of EG10 is connected to GND (ground) in series with temperature protection element 1000. It is connected.
As described in the fourth embodiment, the RL1_OFF signal is HIGH when normal. Since a current flows from intermediate potential V2 to the coil side of relay RL1 through NPN transistor 419, conductors EG9, EG10, and temperature protection element 1000, the contact side of relay RL1 is in a conducting state.

The operation when the heating element 702 abnormally generates heat will be described. Thermistor T11-T7
1. Due to a failure of T12 to T72 or a failure of the CPU, the heater 700 may be overheated to an abnormal temperature due to continuous overheating of the heater 700 without temperature control. In this case, thermal stress is generated in the heater 700, and the heater 700 made of a ceramic plate may be broken, chipped, or cracked. At this time, if the conductor EG9 or the conductor EG10 is disconnected, the current will not flow to the coil side of the relay RL1, so the contact side of the relay RL1 will be in an open state. Therefore, power supply from the AC power supply 25 to the heating element 702 can be turned off.

Also, when the heater 700 abnormally generates heat and the temperature protection element 1000 is released, the current does not flow to the coil side of the relay RL1. can do.

As described above, in this embodiment, the coil side of the relay RL1 is connected in series via the conductors EG9 and EG10 of the heater 700, which are conductive paths to the heater, and the temperature protection element 1000 such as a thermoswitch. connect to. By doing so, the relay RL1 can be turned off when either the conductor EG9, the conductor EG10, or the temperature protection element 1000 is in a released state, so that the protective means can be configured at low cost.

The respective configurations of the above embodiments can be combined with each other as much as possible.

302 Heating element 421 Triac drive circuit T1 to T4 Thermistor 403 Protection circuit 1 404 Protection circuit 2 406 Latch circuit 1 407 Latch circuit 2 408 Abnormal transmission means 1 409 Abnormality transmission means 2, a to d... Abnormality detection circuit

Claims (1)

a heater having a plurality of heat generating blocks that generate heat when energized;
a relay or switching means provided in a power supply path to the heater;
a plurality of triacs provided in power supply paths of the plurality of heat generating blocks ;
a driving unit that drives the plurality of triacs;
a plurality of temperature detection means arranged at a first potential for detecting the temperature of each of the plurality of heat generating blocks ;
a control unit arranged at a second potential insulated from the first potential and configured to control the drive unit based on the temperatures detected by the plurality of temperature detection means;
a plurality of abnormality detection circuit units arranged at the first potential and outputting signals corresponding to temperatures detected by the plurality of temperature detection means;
an abnormality transmission circuit unit that transmits an abnormality of the heater to the relay or switching means based on a signal output from the abnormality detection circuit unit;
An image forming apparatus that fixes an unfixed toner image formed on a recording material to the recording material by heat of the heater and outputs the image,
said relay or switching means being placed at said second potential;
The abnormality transmission circuit unit has an insulated communication means,
The plurality of abnormality detection circuit units are OR-connected to the abnormality transmission circuit unit,
The image forming apparatus according to claim 1, wherein the abnormality transmission circuit section transmits the signal after the OR connection to the relay or the switching means through an insulating communication means.

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